Various controls of an internal combustion engine, such as the air/fuel mixture and compression ratio of combustion chambers, are monitored and adjusted by an electronic control unit. However, to perform the necessary adjustments, the electronic control unit needs current and accurate data from within the combustion chamber. Specifically, pressure data from within each combustion chamber of the engine is highly beneficial when calculating adjustments to the air/fuel mixture or compression ratio to produce a more efficient engine. Accordingly, sensors must be employed in or near the combustion chamber to record such data and transmit the information to the electronic control unit.
In the past, automobile manufacturers have used spring-activated pressure gauges and piezoelectric transducers as combustion chamber pressure sensors. The spring-activated pressure gauges were positioned in a port of the cylinder wall or in a port of the cylinder head of the engine. However, the spring-activated pressure sensing devices did not operate reliably at the high temperatures generally present in the combustion chamber. Further, piezoelectric transducers were also employed as pressure sensors. However, the piezoelectric transducers were also extremely vulnerable to the high temperature environment of the combustion chamber and require cooling via recirculating water or air.
Today, optical fibers are commonly used in pressure sensor assemblies. In operation, strain from an elastic structure, such as a bellows, is transmitted to the sensor via an optic fiber. The connection between the elastic structure and the sensor must be very stable to prevent a phenomenon known as “creep” or a change in strain on the sensing element with no change in applied load on the elastic structure. The “creep” phenomenon distorts the data transmitted to the electronic control unit and unnecessary changes are made to the vehicle's controls. Further, the pressure sensor assembly must be positioned in or near the combustion chamber to collect accurate data. Accordingly, the pressure sensor assembly must withstand the high temperature and high pressure environment present in the combustion chamber in order to provide accurate data to the electronic control unit.
Therefore, a pressure sensor assembly capable of withstanding the harsh environment of the combustion chamber is needed. More specifically, a pressure sensor assembly properly positioned to collect accurate data from the combustion chamber but able to withstand the harsh environment of the combustion chamber is needed in the automotive industry.